Bioluminescence assays and imaging methods have been widely adopted for drug discovery because of their simplicity, robustness, and low-cost. The inherently low background and lack of need for excitation light makes bioluminescence superior to fluorescence methods for many applications. Nevertheless, bioluminescence has yet to reach its full potential. We propose the following specific aims: 1) Expand the scope of bioluminescence imaging with synthetic luciferins; 2) Develop bright and functionally orthogonal luciferases suitable for in vivo imaging; and 3) Leverage ?portable reporters? for imaging in any animal. We will exploit the properties of synthetic luciferin analogs to enhance the imaging of invasive brain tumors, viral infection of the CNS, and circadian rhythms. We will develop fully orthogonal luciferin-luciferase pairs that can serve as internal controls and enable multiplexed imaging. Finally, we will overcome the restricted set of available luciferase-expressing animals by developing bioluminescent reporters that can be introduced into any animal of interest.